The present invention relates to impact tools for use in drilling operations, and more particularly, to fluid actuated percussive drilling equipment such as used in rock drilling and similar operations.
Down hole well drilling, for oil, gas or water, requires a specially designed drill apparatus, which can be used in applications where the diameter of the drill body is less than the drill bit diameter. The drill apparatus must provide high energy output, simplicity, and reliability in order to provide economical operation, and must also be able to withstand the abrasive environment as well as the continuous impact loading required for cutting through rock.
Pressurized fluid actuated impact tools and in particular pneumatic down-the-hole rock drills of this type are generally known, as disclosed in U.S. Pat. No. 4,084,646, the disclosure of which is incorporated herein by reference. This patent discloses a drill having only a single moving part and all valving of the pressurized fluid is accomplished by interior and exterior porting on the piston and the casing. In such known drills, the moving part comprises a piston which strikes directly on the percussive bit. The known devices utilize a piston weighing between 45 and 50 pounds which is reciprocated at a frequency of approximately 1,500-1,800 blows per minute by pressurized air, generally provided at 250 to 350 psi.
The speed at which the drill bit progresses through the rock is dependent upon many factors, including the frequency of the piston movement for impacting on the bit as well as the force with which the piston strikes the bit. The known pneumatic down-the-hole rock drills have been operated successfully for least 20 years. However, in order to reduce the amount of time on site during drilling operations it would desirable to provide an improved drill apparatus which could drill through rock at a higher speed.